1. Field of the Invention
The present invention is broadly concerned with improved, high speed web or sheet processing apparatus designed for extremely accurate registration and operation upon successive material segments fed to the apparatus. More particularly, the invention pertains to such apparatus, and corresponding methods, which are operable for initially gripping or holding a fed material segment, whereupon the gripped segment is essentially simultaneously shifted along orthogonal axes within the plane of the segment, and about a rotational axis transverse to the segment plane for accurate alignment purposes. The invention is particularly suited for high speed accurate die cutting operations.
2. Description of the Prior Art
Three-axis die cutting presses have been proposed in the past for processing of continuous webs. One such press is disclosed in U.S. Pat. No. 4,555,968. The press of this patent includes a shiftable die unit supported on a cushion of air, and the die unit is moved laterally of the direction of travel of the web as well as rotatably about an upright axis perpendicular to the web in order to bring the die unit into precise registration with the defined areas of the web to the die cut by the press. Automatic operation of the press described in the '968 patent is provided by a control system having two groups of photo-optical sensors which are disposed to detect the presence of two T-shaped marks provided on opposite sides of the web adjacent each defined area to be cut. The control system is electrically coupled to servomotor mechanism for adjustably positioning the die unit once advancement of the web is interrupted in a defined area on the web in a generally proximity to work structure of the die unit.
As shown in U.S. Pat. No. 4,697,485, a die cutting press is provided with a registration system operable to provide precise alignment of a shiftable die cutting unit along two axes during the time that the web material is advanced along a third axis to the die unit, so that as soon as a defined area of the web reaches the die unit, the press can be immediately actuated to subject the material to the die cutting operation. Continuous monitoring of an elongated indicator strip provided on the material enables the die unit to be shifted as necessary during web travel to ensure lateral and angular registration prior to the time that web advancement is interrupted.
U.S. Pat. No. 5,212,647 describes a die cutting press provided with a registration system that quickly and accurately aligns defined areas of a web with a movable die unit without requiring the use of elaborate or continuous marks or more than two sensing devices for determining the location of the marks relative to the die unit. The registration system of the '647 patent employs a pair of reference indicia fixed on a bolster of the press for indicating the position at which the indicia on the web of material appear when the defined areas of the web are in a desired predetermined relationship relative to the die unit supported on the bolster.
Application for U.S. patent Ser. No. 08/641,413 filed Apr. 30, 1996 describes an improved die cutting press wherein the entire die unit comprising a lower platen and a shiftable, upper die assembly is supported on a cushion of air. During operation when a defined area of the web is initially fed to the die cutting station, the target area is gripped via a vacuum hold-down and the entire die unit is simultaneous adjusted along three axes so as to achieve precise alignment between the target area on the web and the die cutting assembly.
Although the accuracy provided by such prior art die cutting registration systems is very good, such presses are relatively slow. For example, in the case of the press described in the '413 patent application the necessity of moving the relatively heavy and bulky die assembly tends to slow the operation thereof. The earlier die presses are in general able to operate at speeds no faster than about 20 strokes per minute.
There is accordingly a need in the art for an improved web or sheet-fed processing apparatus, such as a die cutting press, which avoids the problems of prior units of this type and gives very high speed registration and operation.